Dehydration processes of gyrolite

The thermal decomposition processes of natural and synthesized gyrolite, which have a sheet silicate anion structure with Ca/Si molar ratio of 0.66, were compared mainly by ²⁹Si MAS NMR. In the two samples, the silicate anions has the same structure (protonated Q³), however their crystallinity was different. The protonated Q³ structure in both samples decomposed gradually below 800 °C to form nonprotonated monomer (Q⁰) and chain silicate (Q¹ and Q²). Above 900 °C, the natural gyrolite decomposed to pseudo-wollastonite and silica glass, while the synthesized one changed to pseudo-wollastonite and cristobalite via wollastonite. These differences are believed to be caused by the differences in their crystallinity, decomposition rate and the flux effect resulting from the glassification of the impurities.